FEA; When should we activate large deformation?
FEA; When should we activate large deformation?
(OP)
Dear friends.
Can anyone tell me when should i activate large deformation when using finite element analysis?
I have analyzed a pressure vessel's part (Manhole) with steel structure and trying to find out the real deformation in sealing zone. I don't know which is real deformation: Large def= on or off.
Thanks a lot.
Can anyone tell me when should i activate large deformation when using finite element analysis?
I have analyzed a pressure vessel's part (Manhole) with steel structure and trying to find out the real deformation in sealing zone. I don't know which is real deformation: Large def= on or off.
Thanks a lot.





RE: FEA; When should we activate large deformation?
If your stresses are above the yield strength, then also consider including non linear materials (plasticity).
Where codes/standards support design by analysis, the rules are fairly specific (i.e. turn it on).
I've heard people refer to the following rule of thumb: if deformation is >10% of the nominal thickness, then turn it on.
RE: FEA; When should we activate large deformation?
//signed//
Christopher K. Hubley
Mechanical Engineer
Sunpower Incorporated
Athens, Ohio
--
http://engineeringliberty.wordpress.com
RE: FEA; When should we activate large deformation?
RE: FEA; When should we activate large deformation?
- when the displacements of the structure nodes are very large. In these cases, the formulation of the shell elements for bending is no longer valid. I mean... in these element's formulation there is an aproximation: dy/dx=tan(theta)~=theta . This approximation is valid just when there are small displacements. When the large displacement is turned on it's considered that dy/dx=tan(theta). This option should be used when doing FEA of rubber parts, nonlinear elastic analyses, plastic analyses or when the structure displacements are large. It's also recommended to turn it on when the displacement of a plate in out-of-plane bending is bigger than 75% of it's thickness.
- the strain used in the linear FEM formulation is eps=du/dx . However, its an approximation. The real formula, that is used in the nonlinear FEM formulation, have high order terms. These high order terms are considered in the computation of eps when the large displacement is turned on. It's recomended to turn it on when we expect to find large strain, as in rubber parts FEA, in nonlinear elastic analyses or in plastic analyses.